In an advanced information society, there is a demand for the increased capabilities of an information processing device such as a server and a network device such as a router. To meet this demand, it is considered effective to miniaturize LSIs to increase the degree of integration and the degree of integration is expected to steadily increase in the future.
However, while the degree of integration increases, the density of LSI package's signal pins which input and output signals does not increase, thereby preventing an increase in capability. The problem is a so-called “pin bottleneck.”
To solve the above-mentioned pin bottleneck, an attempt is being made to increase the speed of transmitting signals per pin by multiplexing a plurality of signals (parallel-to-serial conversion) inside LSI. Owing to the multiplexing technique, transmission speed has increased to around 10 Gbps. The increased speed, however, cause various problems. For example, transmission loss increases due to skin effect on the lines of a circuit board. In this case, because of the deterioration of transmission characteristics, an additional circuit such as a waveform correction circuit is necessary to improve transmission characteristics even for transmission of several dozen centimeters. As a result, problems that circuits become complex and power consumption increases are brought.
To solve the above-mentioned problems, an optical connection technique is being developed to convert the output of LSI into an optical beam before transmission. The optical connection of high-speed signals at around 10 Gbps has been primarily used between bodies of large-scale devices. This sort of connection is expected to be used for among cards inside devices, for backplanes, and for wiring between LSIs on a board in the future.
Moreover, as a technique for realizing optical connection between LSIs, a technique of forming an optical waveguide on an optical electronic integrated structure where LSIs and photoelectric conversion devices are integrated or an electrical circuit board is increasingly examined. Research and development on the technique has been conducted worldwide particularly as a surface emitting laser, which is small and can be arrayed, is put to practical use.
For example, an optical electronic integrated structure where optical waveguides, photoelectric conversion elements and LSIs are integrated and information is exchanged therebetween is disclosed in NPL 1 described later. FIG. 3 shows the configuration of the optical electronic integrated structure disclosed in the literature.
The optical electronic integrated structure shown in FIG. 3 is a structure where a LSI 105, an photoelectric conversion device, and a driver IC which drives the optical device are integrated on an interposer 106. In the structure, a transmitting section on the left side of the diagram converts an output signal of the LSI 105 into an optical signal at a surface emitting laser array (VCSEL array) 103, and transmits the optical signal through a polymer waveguide 102 formed on a printed-circuit board (PCB) 101. A receiving section on the right side of the diagram converts the optical signal from the transmitting section into an electric signal using a photodiode array (PD array) 104, which is a light receiving element, and inputs the electric signal into the LSI 105.
Moreover, techniques for transmitting information using similar optical electronic integrated structures to the one shown in FIG. 1 are disclosed in PTLs 1, 2, 3 and 4 described later.
[Citation List]
[Patent Literature]
[PTL 1] JP-A-2000-114581
[PTL 2] JP-A-2004-274155
[PTL 3] JP-A-05-333396
[PTL 4] JP-A-05-067770
[PTL 5] JP-A-2003-309520
[Non Patent Literature]
[NPL 1] Ishii et al., “SMT-Compatible optical-I/O Chip Packaging for Chip-Level Optical Interconnects”, Electronic Components and Technology Conference 2001, p. 870